High-purity ferritic stainless steel sheet with excellent oxidation resistance and high-temperature strength, and process for producing the same

Abstract

The present invention provides a low-alloy high-purity ferritic stainless steel sheet provided with improved oxidation resistance and high-temperature strength by utilizing Sn addition in trace amounts without relying on excessive alloying of Al and Si which reduces fabricability and weldability or addition of rare elements such as Nb, Mo, W, and rare earths, and a process for producing the same. The high-purity ferritic stainless steel sheet includes C: 0.001 to 0.03%, Si: 0.01 to 2%, Mn: 0.01 to 1.5%, P: 0.005 to 0.05%, S: 0.0001 to 0.01%, Cr: 16 to 30%, N: 0.001 to 0.03%, Al: 0.05 to 3%, and Sn: 0.01 to 1% (% by mass), with the remainder being Fe and unavoidable impurities. A stainless steel slab having such steel components is heated, wherein an extraction temperature is 1100 to 1250° C., and a winding temperature after hot rolling is 650° C. or lower. A hot-rolled sheet is annealed at 900 to 1050° C., and cooled at 10° C./sec or less over a temperature range of 550 to 850° C.

The invention claimed is: 
     
       1. A ferritic stainless steel sheet, consisting of, in % by mass, C: 0.001 to 0.03%, Si: 0.01 to 2%, Mn: 0.01 to 1.5%, P: 0.032% or less, S: 0.0001 to 0.01%, Cr: 16 to 30%, N: 0.001 to 0.03%, Al: 0.155 to 3%, and Sn: 0.01 to 1%, with the remainder being Fe and unavoidable impurities, and having a 0.2% proof stress of 35 MPa or more and a tensile strength of 65 Mpa or more at 800° C., and
 wherein the ferritic stainless steel sheet has oxidation resistance which does not cause unusual oxidation in a continuous oxidation test at 980° C. for 200 hr. 
 
     
     
       2. A ferritic stainless steel sheet, consisting of, in % by mass, C: 0.001 to 0.03%, Si: 0.01 to 2%, Mn: 0.01 to 1.5%, P: 0.032% or less, S: 0.0001 to 0.01%, Cr: 16 to 30%, N: 0.001 to 0.03%, Al: 0.055 to 3%, and Sn: 0.01 to 1%, and
 one or more of Nb: 0.18% or less, Ti: 0.5% or less, Ni: 0.5% or less, Cu: 0.5% or less, Mo: 0.5% or less, V: 0.5% or less, Zr: 0.5% or less, Co: 0.5% or less, Mg: 0.005% or less, B: 0.005% or less, Ca: 0.005% or less, La: 0.1% or less, Y: 0.1% or less, Hf: 0.1% or less, and REM: 0.1% or less, with the remainder being Fe and unavoidable impurities, and having a 0.2% proof stress of 35 MPa or more and a tensile strength of 65 Mpa or more at 800° C., and 
 wherein the ferritic stainless steel sheet has oxidation resistance which does not cause unusual oxidation in a continuous oxidation test at 980° C. for 200 hr. 
 
     
     
       3. A process for producing a ferritic stainless steel sheet, comprising heating a stainless steel slab having the steel components according to  claim 1  or  2 , wherein an extraction temperature is 1100 to 1250° C., and a winding temperature after hot rolling is 600° C. or lower. 
     
     
       4. The process for producing the ferritic stainless steel sheet according to  claim 3 , comprising annealing the steel sheet at 900 to 1050° C., and then cooling the annealed steel sheet at 5° C./sec or less over a temperature range of 550 to 850° C. 
     
     
       5. The ferritic stainless steel sheet according to  claim 1  or  2 , wherein the C content in the steel sheet is 0.004 to 0.007%. 
     
     
       6. The ferritic stainless steel sheet according to  claim 5 , wherein the Al content in the steel sheet is more than 0.8% to 3%. 
     
     
       7. A process for producing a ferritic stainless steel sheet, including heating a stainless steel slab having the steel components according to  claim 5 , wherein an extraction temperature is 1100 to 1250° C., and a winding temperature after hot rolling is 600° C. or lower. 
     
     
       8. The process for producing the ferritic stainless steel sheet according to  claim 7 , including annealing the steel sheet at 900 to 1050° C., and then cooling the annealed steel sheet at 5° C./sec or less over a temperature range of 550 to 850° C. 
     
     
       9. The ferritic stainless steel sheet according to  claim 1  or  2 , wherein the Al content in the steel sheet is 0.155 to 1.3%. 
     
     
       10. A process for producing a ferritic stainless steel sheet, including heating a stainless steel slab having the steel components according to  claim 9 , wherein an extraction temperature is 1100 to 1250° C., and a winding temperature after hot rolling is 600° C. or lower. 
     
     
       11. The process for producing the ferritic stainless steel sheet according to  claim 10 , including annealing the steel sheet at 900 to 1050° C., and then cooling the annealed steel sheet at 5° C./sec or less over a temperature range of 550 to 850° C. 
     
     
       12. The ferritic stainless steel sheet according to  claim 1  or  2 , wherein the Al content in the steel sheet is more than 0.8% to 3%.